In recent years, portable terminals such as portable wireless phones are widely spread and a user can easily view Web pages or animations such as broadcast programs via a portable terminal while he/she is out.
When the Web pages or animations are viewed, a display screen on the portable terminal is smaller than the screen of a personal computer or television, and thus the portable terminal displays image data or the like compressed based on the size of the display screen on the display screen. For example, a technique of a portable terminal described later is disclosed in Patent Literature 1, for example. When received original image data has a larger number of pixels than the display unit, the portable terminal reduces the number of pixels of the original image data to the number of pixels of the display unit for display. When a position is designated on the image by a pointing device, a corresponding coordinate in the original image data is calculated and an image region having the same number of pixels as that of the display unit is designated in the original image data on the basis of the corresponding coordinate and its information is transmitted to an image data distributing device. Thereby, when image data corresponding to an image region is received, the image region is displayed as a partially-enlarged image on the display unit without changing the number of pixels of the image data.